1. Technical Field
The present invention relates to image determining apparatuses, image enhancement apparatuses, backlight image enhancement apparatuses and backlight image enhancement methods.
2. Related Art
Various kinds of image reading apparatuses, such as image scanners, ordinarily can be connected by wire or wirelessly to a computer system, such as a personal computer, to send images read in from original documents as image data to the computer system. The computer system receives the image data that has been sent from the image reading apparatus and stores it in a data storage device, such as a memory or a hard-disk drive. In the course of this, the computer system performs various kinds of adjustment processing on the image data that has been sent from the image reading apparatus.
As an adjustment process that can be carried out, there is for example a histogram adjustment for adjusting the brightness of the image or a density enhancement, in which the darkness/brightness of the image is partially changed. Such adjustments are automatically carried out by various programs, such as a driver program or application program for the image reading apparatus installed on the computer system, or they are carried out by the user or the like. Other than that, there are also adjustments for enhancing a backlight image, for example. As such backlight enhancement methods, various methods have been proposed (for example JP-A-H10-79885, JP-A-2004-56416 and JP-A-2000-134467).
(1) Now, in the conventional methods for enhancing a backlight image, it was not possible to carry out a sufficient enhancement process on images in which the color balance of, for example, a sunset or a sunrise is destroyed. That is to say, in the case of images in which the color balance of, for example, a sunset or a sunrise is destroyed, it was necessary to carry out an enhancement process that is suited for such images. And in order to carry out such an enhancement process, it was necessary to accurately determine whether the image to be enhanced is in fact an image in which the color balance of a sunset or a sunrise is destroyed, for example.
(2) In the conventional methods for enhancing a backlight image, it was not possible to carry out a sufficient enhancement process on images in which the color balance of, for example, a sunset or a sunrise is destroyed. That is to say, in conventional enhancement methods, it was not possible to achieve a sufficient improvement of image quality for such images in which the color balance of, for example, a sunset or a sunrise is destroyed. Accordingly, there is a need for an enhancement process that is suitable for such images in which the color balance of, for example, a sunset or a sunrise is destroyed.
(3) A backlight image includes a backlight image in which the color balance of, for example, intermediate tones is destroyed and a backlight image of a sunset or a sunrise. However, with a backlight image enhancement method proposed conventionally, it was not possible to perform sufficient enhancement to a backlight image in which the color balance of, for example, intermediate tones is destroyed and a backlight image of a sunset or a sunrise. That is, a backlight image in which the color balance of, for example, intermediate tones is destroyed and an image of a sunset or a sunrise have different characteristics to a normal backlight image. Thus, it was necessary to perform an enhancement process that was suitable for the image in which the color balance of, for example, intermediate tones is destroyed and an image of a sunset or a sunrise.